In recent years, solar photovoltaic technology has been significantly developed and various solar cells are commercially distributed. The solar photovoltaic power generation of “converts light energy from the sun into electric energy” has such advantages that (1) the energy source is enormous and is not depleted; (2) the energy source is clean and carbon dioxide is not generated during power generation; and (3) it allows energy self-sufficiency, and it is technology that can be used not only outside but also in space. The solar cells are roughly classified into the ones containing a silicon semiconductor (crystalline and amorphous (noncrystalline)) as a material and the ones containing a compound semiconductor as a material and cover more various types including those under development.
However, current solar cells can generate only low electricity despite the high production cost, and result in very low cost effectiveness compared to conventional power generation systems. In addition, solar cells after long-term use are observed to have degradation phenomena such as yellowing, separation, whitening and the like of sealing materials due to sunlight and moisture. Therefore currently the solar cells are required to have a long operating life as well as improved maximum power output.
As one of the currently proposed methods for long operating life of a solar cell, measures for preventing degradation have been confered by adding an ultraviolet absorber, a light stabilizer and an antioxidant to a sealing material.
In order to improve the maximum power output, maximum power point tracking (MPPT) which allows the maximum power output to be obtained by maintaining an optimal operating point according to the variation in the incident light intensity has been widely used (Non-Patent Document 1).